Guy left his car running when he ran into a store the other day. I saw it and drove it away. Nobody said anything. Guess it's OK.

Seriously, OP knows it's theft of services. He just got away with it. Maybe next time he'll get caught. Who knows.

Are we really doing this again?

Yup. This is exactly the same as sitting in an unoccupied row of a plane. Great analogy.

Wow some of these responses are so odd. How is it stealing switching seats on an half empty flight? FA's are some of the most no nonsense people out there. If they had a problem with it, it would've been made known. I once got sat in Business class on a long haul because my legs were hurting me. Did I steal the seat? I mean I didn't pay for it.

While I doubt the airline would pursue it that far, the OP could be criminally charged with Theft of Service. Your sentence above should be corrected to say "If they had a problem and noticed it, it would've been made known". Stealing and getting away with it is still stealing.

I understand your point of view, I just don't agree with it. Calling it stealing implies that the airline had a direct loss because of it. The flight commenced they weren't going to make money on that seat. I guess this is one of these grey areas that people aren't going to see eye to eye on.

the never-ending debate between situational ethics and "choose your battles"

It's more than just a point of view. Had the airline caught him and decided to pursue it, he could have been charged with a crime. That's not a gray area.

Analogy: Once a movie starts and the theater isn't selling anymore tickets, can I sneak in the back door? After all, they weren't going to make any money on me.

Consuming something you didn't pay for, knowing that there is a cost attached to it and that you are supposed to pay for it, is not "situational". It does fall under the "choose your battles", though.

The grey area I was alluding to was the difference in opinion amongst the members here not the law. Your analogy doesn't really fit because you are saying you didn't buy a ticket and are sneaking in. A more proper analogy would be you bought movie tickets changed your mind and went into a different movie than the one you originally chose.

A movie that cost a lot more than the one you bought the ticket for, to make a proper analogy. Or buying standing room only at a concert and then heading for a vacant front row seat.

It's theft.

Okay I concede, no changing opinions here. Lets all be cops and go after these thieves. They are ruining the economy.

I must have missed the posts where anyone said that.

I take it your opinion is that it's a perfectly honest thing to do.

IBTL

It is something that I have never done, I just think calling someone a thief for switching seats is quite harsh and a little silly.

Very simple. if I pay for the privilege of sitting in E+ (either by spending $$ directly, or by spending lots of $$ to get status and thus free E+), it's gonna annoy the hell out of me if someone comes up and just takes it without paying for it.
If you don't like the concept of E+ and E-: go fly southwest.

Let's complete your sentence and try again. "switching seats into a more expensive seat that he knew was more expensive and he did it hoping he wouldn't get caught..."

At the beginning of every UA flight I've been on the past few years the FAs make an announcement that you cannot move into an E+ seat and that if you want to use an E+ seat please let the FA know and she will arrange payment.

It's theft. Pure and simple.